CATALYSIS AND CATALYSTS 207 



required in these operations is a question of great practical 

 importance which will be dealt with in a later chapter. It is 

 only necessary to say here that the hydrogen employed must be 

 approximately pure, as the presence of small quantities of 

 sulphur or arsenic compounds serves to diminish the activity of 

 the catalyst, and ultimately to destroy it, as in other cases 

 already referred to. Though the weight of hydrogen actually 

 absorbed by the oil is relatively small, the volume of gas, by 

 reason of its lightness, assumes enormous proportions. One ton 

 of oleic acid requires roughly 79,000 litres or 2800 cubic feet, 

 and one ton of ordinary olein requires 75,900 litres or 2680 cubic 

 feet of hydrogen gas. 



It is also of the utmost importance to prepare the catalyst, 

 usually reduced nickel, in such a way as to avoid the intro- 

 duction of impurities. Thus it is found that when the hydroxide 

 of nickel from which the metal is to be reduced has been made 

 from the sulphate, it is impossible to avoid the presence of 

 minute quantities of basic sulphate, and when this is heated in 

 hydrogen it is reduced to sulphide and the resulting metal is 

 ruined so far as its catalytic power is concerned. 



An interesting method of introducing a very active form of 

 catalyst is based on the remarkable power possessed by nickel 

 of uniting with carbonic oxide to form a volatile compound. 

 According to this process water gas, a mixture of hydrogen and 

 carbonic oxide, is passed over nickel ore at about 100 C. The 

 carbonic oxide unites with the nickel, leaving other metals 

 behind, and nickel tetracarbonyl, Ni(CO) 4 , is produced in any 

 required amount. This compound in vapour together with the 

 excess of hydrogen is then passed into the liquid to be hydro- 

 genated at a temperature between 200 and 240 C., when the 

 nickel carbonyl is decomposed, depositing the metal in a finely 

 divided and very active state. It is probably at the moment 

 when it is liberated from the compound that the nickel causes 

 the union of the hydrogen with the fat, as it is stated that if the 

 carbonyl compound is first passed in so that the nickel is liberated 

 and the hydrogen is then supplied no practical result is obtained. 



The application of the process is not confined to soap and 

 candle making. Already various inferior oils are being converted 

 into solid fats which, after due purification, are transformed into 

 edible products, and in all probability considerable additions to 

 |:he supply of margarine from the chemical factory may be 



